Facility Runoff

• Received Digital Terrain Model in tin format

  • # of triangles = 421,472
  • Planimetric area = 22,645,058 sq. ft.
  • Surface area = 22,954,375 sq. ft.
  • Average area of a triangle = 54 sq. ft.

• Converted the tin to a grid (DEM) with a 3 ft. cell size

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The next step was to characterize runoff at the actual facility. I received a digital terrain model in tin format from Air Survey Corporation, who is providing the basemap coverages and photos. There are 421,000 triangles that comprise the tin, and when you divide the surface area by the # of triangles, you find that the average triangle has a size of 54 sq. ft. This area would correspond to a grid cell size of 7.5 ft. I played around with a lot of different cell sizes. You don’t want to use the average size, but you also don’t want to use the size of the smallest triangle. I thought 3 ft. was a pretty good value and I converted the tin to a grid using built-in functions of 3-D Analyst. You can also use ArcInfo.